The present invention relates to magnetic tape cassettes, and more particularly to a magnetic tape cassette having improved tape guides which are brought into sliding contact with a magnetic tape to guide the latter.
In an audio or video magnetic tape cassette, tape guides are provided on both (right and left) sides of the front opening of the cassette, and the guides are brought into sliding contact with the rear surface (base) of the magnetic tape to guide the latter. In an audio magnetic tape cassette, the tape guides are usually made of plastic resin and are integral with one of the cassette halves. However, recently, cylindrical metal tape guides have been extensively employed, which guides are fitted in the cassettes. The metal tape guides can maintain the initial characteristics of the tape, for instance, the tape sliding characteristic, satisfactory for a long period. Video magnetic tape cassettes generally use such cylindrical metal tape guides.
Difficulties accompanying a conventional magnetic tape cassette will be described with reference to FIG. 1 which shows the fundamental structure and the arrangement of metal tape guides of a type extensively employed in video tape cassettes or the like.
The tape guide 11 shown in FIG. 1 is in the form of a cylinder, the outer wall 2 of which is brought into sliding contact with the base surface of a magnetic tape to guide the latter. During the assembling of the magnetic tape-cassette, the tape guide 11 is fitted on a lower guide post 8 which is integrally formed on the lower half case 6. If the tape guide 11 is excessively tightly fitted on the lower guide post 8, the outer wall of the lower guide post 8 may be scraped away, or the tape guide 11 may be deformed, or at worst broken, depending on the material. Especially in the case where the tape guide 11 is formed by curving a plate-shaped material, the joint may be opened, thus deforming the tape guide.
After the tape guide 11 is engaged with the lower guide post 8 on the lower half case 6, the upper half case 7, carrying an upper guide post 9 to be inserted into the tape guide 11, is placed on the lower half case 5. The tape guide 11 is fixedly secured in the cassette, for instance, with a screw 10 which is screwed into the upper guide post 9 through a through-hole 8a in the lower guide post 8.
When the upper and lower half cases 6 and 7 are combined together, sometimes the tape guide 11 is tilted. In other words, due to the molding process, the upper and lower half cases 6 and 7 may have dimensions which vary, and therefore the two guide posts 8 and 9 are liable to be displaced, which may tilt the tape guide 11. In addition, the molded upper and lower half cases are liable to be nonuniform in thickness, that is, the inner walls of the cassette, which are in contact with the tape guide, are liable not to be completely flat. Therefore, sometimes the tape guide may come into a sloping position during assembly. If the tape guide 11 is inclined with respect to the cassette, the tape running path is unstable and the tape running characteristic is lowered.
For a cassette incorporating a metal tape or vacuum-deposited tape suitable for high density recording and reproducing, it is preferable to use ceramic tape-guides having an excellent physical strength (wear resistance) instead of the above-described conventional tape guides made of metal because, where the former tape guides are employed, the magnetic tape is less deteriorated in certain characteristics and attains an excellent running performance. However, the ceramic tape guide is still disadvantageous in that it is difficult to form a cylindrical ceramic tape guide, the wall is liable to be broken, and it is considerably difficult to set the ceramic tape guides in the cassette.